The sulfhydryl-disulfide status of tubulin will be examined in several situations. Diamide treated tubulin shows aggregation at room temperature and above and at high protein concentration at low temperature. We have shown this to be due to disulfide formation and we will now examine the nature of the intramolecular and intermolecular disulfides which may be formed. We will continue our studies of sulfhydryl-disulfide status of tubulin in pool tubulin and membrane bound tubulin in dividing eggs as a function of the cell cycle. We will continue studies of the configuration changes induced by diamide and especially their rates of occurrence. We will continue studies of the nature of the activation of glutathione reductase in marine eggs and of several thioltransferases which can be affected by caffeine. In addition we will continue studies of the relation of glutathione levels to microtubule assembly in eggs. We will also continue studies of the relation of glutathione, NADPH, glutathione reductase and NAD-kinase to microtubules in DBCAMP and cholera toxin treated CHO cells. Finally, we will extend our studies of the intracellular sites of binding of phenyl glyoxal. BIBLIOGRAPHIC REFERENCES: Nath, J. and L.I. Rebhun. (1976). J. Cell Biol. 70, 43a. Effects of diamide and N-ethyl maleimide on metabolism and cell division in sea urchin eggs. Rebhun, L.I. (1976). J. Cell Biol. 70, 44a. Tubulin polymerizability and sulfhydryl disulfide state: A possible in vivo mechanism.